Genetic testing. What? How? Why? And is it playing God?
What is Genetic Testing? There are two types of genetic testing that can be done on embryos. Both genetic tests are preformed on a day 3 or 5 prior to the embryo being transferred into the uterus. The distinction between the two types of testing: PGD and PGS.
- PGD, preimplantation genetic diagnosis, involves removing a cell from an IVF embryo to test it for a specific genetic condition (cystic fibrosis, genetic disorders, cancer, for example) before transferring the embryo to the uterus.
- PGS, preimplantation genetic screening, is the proper term for testing for overall chromosomal normalcy in embryos. PGS is not looking for a specific disease diagnosis – it is screening the embryo for normal chromosome numbers.
PGS is the more common genetic testing done in IVF. It basically tests for down-syndrome and sex chromosomal abnormalities (i.e. embryos with an extra sex chromosome). These are the two types of chromosome abnormalities that can result in a live birth- all other genetic chromosome abnormalities usually end in miscarriage or never lead to a viable pregnancy.
How is this process done? After the eggs are retrieved, they are then fertilized using ICSI. For 3 to 5 days these embryos will continue to grow and split. The embryos that are at the appropriate stage will be sent off for these genetic tests. We will be doing a biopsy called trophectoderm biopsy, which is performed on day 5 or 6 of embryo development. It is performed at the blastocyst stage after the embryo has differentiated into an inner cell mass, a trophectoderm component and a fluid filled cavity. With trophectoderm biopsy at the blastocyst stage a small hole is made in the shell of the embryo and several cells that are precursors to the placenta (trophectoderm) are removed for testing
- This technique has shown promising results in US IVF programs. It is now considered by many experts to be the biopsy procedure of choice for PGD and PGS testing.
- Genetic testing, like many medical procedures, is not 100%. Embryo’s can be damaged in the process of collecting the cells, and can be graded abnormal when normal or visa versa.
Why genetic testing?
In general, there are 5 main groups of patients that might utilize PGS or PGD.
- Patients that are having IVF with advanced female age – 38 or older (common)
- Patients of any age with repeated IVF failure – usually defined as 3 or more failed attempts
- To screen for inherited genetic diseases
- Patients that are carriers of chromosomal translocations
- Patients that have had recurrent miscarriages
PGD / PGS and Age – aneuploidy screening (PGS) – checking the chromosomes
- The most common reason that PGS is done in the US is for “advanced age”.
- This would often mean older than about 37 in many programs offering PGD.
- The logic relates to the fact that women of advancing age have increased rates of chromosomally abnormal eggs – which after fertilization will become chromosomally abnormal embryos.
Human eggs are often chromosomally abnormal – and the percentage of eggs with a chromosomal abnormality increases with increasing female age. In general, about 30-60% of human embryos have some type of chromosomal abnormality. This increases significantly with advancing female age.
Furthermore, in an IVF cycle that is not doing genetic testing they will grade growing embryos on day 3. Healthy graded embryos will be transferred and/or frozen on day 3. Embryos with genetic abnormalities can look healthy from the outside- you would only know if they were abnormal by looking inside (genetic testing). The potential for transferring a genetically abnormal embryo is pretty high. These pregnancies usually end in early miscarriage. For example with our first IVF, cycle before our eggs were sent to genetic testing, we had 4 embryos that were graded good/good (which is the highest grade they can receive). Out of those 4 that were then genetically tested, we only had 1 normal egg. ONE. This raised a red flag for us and our doctors and is one of the reasons why we have decided to do genetic testing again with these 2 IVF cycles.
We decided to do genetic testing for a few reasons. 1. With the diagnosis of Low AMH my eggs are at higher risk of being chromosomally abnormal. (please click link for more info about AMH). 2. When doing genetic testing, you decrease your chance of miscarriage significantly. Miscarriage usually occurs because there is a chromosomal abnormality in the fetus. We have already been through so much I don’t know what would happen if we got all the way to a pregnancy and then I lost the baby. 3. It increases IVF success. 4. If given the option with genetic testing to bring a healthy child vs. an unhealthy child into the world, we wanted a healthy child. Not that an unhealthy child would be loved any less, but given the option we would go with the obvious. Which brings me to…
Is genetic testing playing God? I don’t know. This is a hard question. God created the world and life, so didn’t he create and give us medicine as well? Genetic testing has definitely opened the discussion for ethical and social issues. As of now genetic testing is solely used to weed out chromosomally abnormal embryos and embryos that have genetic diseases. With that said, genetic testing does supply you with the gender of your healthy embryo’s, which could lead to gender selection. You do not have to find out the gender if you do not want to, but the information is there for you. Hubs and I want to transfer one healthy boy and one healthy girl. I guess that would be considered gender selection… At some point in the future, tests will no doubt be marketed for genes that are associated with behavioral traits such as intelligence, sexual orientation, possibly even perfect musical pitch, or physical characteristics like height, hair color and eye color. A way for a parents to create a so- called “designer baby”. Many of these claims will be highly questionable. And what about gene mutations that have, say, a 20% or 30% chance of causing disease when the child is in midlife? Should parents discard an embryo based on that percentage? Consequently, over time, certain disease will become relegated to certain social groups, but not others. The gap between the wealthiest 1% and everyone else is already expanding. Should we allow this method to widen it more in the genetic pool? Others see this technology as raising troubling issues of eugenics, which had horrific results under the Nazis, who sought to “purify” the gene pool in Germany, and eliminate people whom they felt were genetically inferior. I know I am talking a little extreme, but with the way science and the world are heading this is a big topic of debate. I just pray that doctors remain moral and ethical with the use of these tests.
My husband is devout in his faith. It took him a while to get on board with IVF, because at first he felt that IVF was “like playing God”. Obviously, after he learned more about the process, he was all for IVF to start a family. Myself on the other hand, I have my faith, but I am more “spiritual”. I didn’t know if I really wanted to do genetic testing. My husband was the one really pushing for it. I think it’s a bit ironic. I am glad we did genetic testing on our last IVF cycle. If we would not have, our journey would have been quite different and would have cost us a lot more money, time, and energy. This time around we are doing genetic testing again because of how many abnormal embryo’s we had during our last IVF cycle. If God blessed us with a child with special needs we would love and care for that child like no other, but we feel that because we have the opportunity to do genetic testing it would be unfair to bring a child into this world with health issues, when we can prevent it. Not all will feel the same. Some will downright think it is wrong. But, this is our journey…
“How beauteous mankind is,” Shakespeare’s Miranda exclaims optimistically in “The Tempest.” “Oh brave new world, that has such people in it!” Huxley used these words ironically. Between her hope and his pessimism may lie the reality.
source: CNN, Advancedfertility